Generate Hydra Fastfetch emblem and verify packaged ASCII art

assets/branding/README.md

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+# Hydra OS mark
+
+`hydra-mark.png` is the original transparent image generated with the built-in
+imagegen tool. The complete prompt and conversion settings are in
+[`generation.json`](generation.json). `preview.png` shows the resulting ASCII
+glyphs; the shipped asset is `image/rootfs/usr/share/hydra/fastfetch.txt`.
+
+The 44-column mark uses ordinary ASCII characters, cyan Fastfetch color `$1`,
+and a white `$2` caption. Pillow is needed only to regenerate the text, not to
+run Fastfetch or build an image with the checked-in asset.
+
+From the repository root, with Python and Pillow available:
+
+```sh
+python3 dev/render-logo.py
+fastfetch --config image/rootfs/etc/fastfetch/config.jsonc \
+  --logo image/rootfs/usr/share/hydra/fastfetch.txt --pipe false
+```
+
+On a Nix development host, the converter can also run in a temporary environment:
+
+```sh
+nix-shell -p 'python3.withPackages (p: [p.pillow])' \
+  --run 'python3 dev/render-logo.py'
+```
+
+The converter uses opacity to preserve the single-color silhouette, removes
+faint alpha noise, and accounts for terminal character proportions. It preserves
+the PNG source. Future ISO builds and runtime update bundles include the new text;
+previously built ISOs and installed guests retain their existing logo.